Kronecker delta

In mathematics, the Kronecker delta (named after Leopold Kronecker) is a function of two variables, usually just non-negative integers. The function is 1 if the variables are equal, and 0 otherwise:

This latter case is for convenience.

Properties

The following equations are satisfied:

Therefore, the matrix δ can be considered as an identity matrix.

Another useful representation is the following form:

This can be derived using the formula for the finite geometric series.

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